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Manganese Oxide Minerals: Crystal Structures and Economic and Environmental Significance
Abstract
Manganese oxide minerals have been used for thousands of years-by the ancients for pigments and to clarify glass, and today as ores of Mn metal, catalysts, and battery material. More than 30 Mn oxide minerals occur in a wide variety of geological settings. They are major components of Mn nodules that pave huge areas of the ocean floor and bottoms of many fresh-water lakes. Mn oxide minerals are ubiquitous in soils and sediments and participate in a variety of chemical reactions that affect groundwater and bulk soil composition. Their typical occurrence as fine-grained mixtures makes it difficult to study their atomic structures and crystal chemistries. In recent years, however, investigations using transmission electron microscopy and powder x-ray and neutron diffraction methods have provided important new insights into the structures and properties of these materials. The crystal structures for todorokite and birnessite, two of the more common Mn oxide minerals in terrestrial deposits and ocean nodules, were determined by using powder x-ray diffraction data and the Rietveld refinement method. Because of the large tunnels in todorokite and related structures there is considerable interest in the use of these materials and synthetic analogues as catalysts and cation exchange agents. Birnessite-group minerals have layer structures and readily undergo oxidation reduction and cation-exchange reactions and play a major role in controlling groundwater chemistry.
... Its oxides are ubiquitous in the environment. Composed of manganese in varying oxidation states and oxygen, they range from the rutile-structured MnO 2 and its polymorphs, to haussmanite Mn 2,3+ 3 O 4 , Mn 3+ 2 O 3 and hydroxides, through to complex, layered or tunnel-structured Mn 3+,4+ minerals like todorokite and birnessite [23]. Table 1 gives an overview of the many naturally occurring manganese oxides (MnOx). ...
... Additionally, MnOx are frequently less toxic to the environment than materials used in comparable applications (e.g. V 2 O 5 in catalysts) and it is an abundant resource [23]. Accordingly, the synthesis of MnOx has been studied extensively in well-controlled settings (e.g. ...
... Important Mn oxide minerals and examples of their occurrence and applications.Source:[23]. ...
... Manganese oxides are commonly found in soils [1,2], typically as a minor component but their presence can significantly impact certain soil properties. While manganese oxides can be found in a variety of compositions ranging from MnO to MnO 2 , it is found that only the more oxidized forms have been seen in soils. ...
... Within soil minerals, manganese primarily exists in the quadrivalent state; however, there is also a substitution of Mn 2þ and Mn 3þ for Mn 4þ , which is balanced by the replacement of O 2À ions with OH À ions. Birnessite ((Na,Ca)Mn 7 O 14 .2.8H 2 O), lithiophorite (LiAl 2 (Mn 2 4þ Mn 3þ )O 6 (OH) 6 ), hollandite (Ba x (Mn 4þ ,Mn 3þ ) 8 O 16 ), todorokite ((Ca,Na,K) x (Mn 4þ ,Mn 3þ ) 6 O 12 .3.5H 2 O), and pyrolusite (β-MnO 2 ) are the manganese-based mineral compositions found in soils [2]. Relating to phase formation, manganese oxides are considered to be the most complex of all other metallic elements [3][4][5][6]. ...
... Manganese oxide is renowned for its remarkable versatility among transition metal oxides due to its capacity to achieve oxidation states ranging from þ4 to þ2. Depending on the temperature and oxygen partial pressure, manganese can give rise to various oxides of MnO, MnO [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Mn 2 O 3 possesses a broad spectrum of uses [6,7,10,11,13,15,16], particularly in the realm of fabric printing and dyeing processes. ...
In this work, few precursors (MnCl2.4H2O, MnCO3, MnO2, and KMnO4) were simply heated at 650ºC for 10 hours and examined their phase formation and thermal features of Mn-based oxides. Cubic Mn2O3 phase materials with space group, Ia-3 (206) formed for the heat treated products of MnCl2.4H2O and MnO2 precursors. However, the purity is differed for the heat treated product of MnCl2.4H2O, for this three weak impurities are noted along with the major Mn2O3 phase. Mixed phases of Mn2O3 and Mn5O8 were observed for the heating of MnCO3 precursor. The resemblance of δ-MnO2 phase was observed for the heat treated product of KMnO4 precursors. While the heat treated products of MnCl2.4H2O, MnCO3, and MnO2 precursors show the low weight loss of 1.5 – 3.3 %, the heat treated KMnO4 precursor shows relatively high weight loss of 22.6 % with weak exothermic and endothermic peaks at 100 and 797°C, respectively. The Mn2O3 nanomaterials exhibit a morphology resembling nanorods.
... Manganese oxides are well known for a wide range of applications, such as wastewater treatment [1], metal adsorption ( [2,3]), energy storage applications, and rechargeable lithium batteries [4]. However, the mineral identification of manganese oxide minerals remains challenging due to their nano-crystallinity and their structural and oxidation-state diversity from Mn 2+ to Mn 7+ [5]. ...
... All the potentials reported are expressed vs. Ag/AgCl. Figure 1a) or also known as γ-MnO 2 , which consists of an intergrowth structure of β-MnO 2 type tunnels [1 × 1] as well as ramsdellite type tunnels [2 × 1] ( [5,10]). X-ray diffraction analysis of the heat-treated sample clearly indicates that the primary nsutite successfully transformed into a well-crystallized hausmannite ( Figure 1b). ...
... Analysis of the XRD patterns of natural manganese oxide shows that the 2θ valu of 22.4°, 23.7°, 34.45°, 36.95°, 38.61°, 40.7°, 42.36°, 43.68°, 55.95°, 57.5°, and 61.81° were a tributed to the mineral phase of nsutite (Figure 1a) or also known as γ-MnO2, which co sists of an intergrowth structure of β-MnO2 type tunnels [1 × 1] as well as ramsdellite typ tunnels [2 × 1] ( [5,10]). X-ray diffraction analysis of the heat-treated sample clearly ind cates that the primary nsutite successfully transformed into a well-crystallized hau mannite (Figure 1b). Figure 2 shows the cyclic voltammograms of MXL3 (natural nsutite) and MXL3H (heat-treated nsutite) electrodes with a sweep rate of 50 mV/s in potential windows of (− 0.8) and (−1, 1), respectively. ...
... Manganese(Mn)-oxides are extensively studied because they are one of the strongest natural oxidants and sorbents in aquatic and terrestrial systems (Post, 1999;Ying et al., 2012). These ubiquitous natural minerals alter nutrient, organic matter, and contaminant cycling in the environment (Manceau et al., 2002;Vodyanitskii et al., 2004). ...
... The structure and composition of Mn-oxides determine their chemical properties. MnO 6 octahedra are the building blocks of Mn-oxides which are often arranged in a tunnel or layered structure and connected by edge and corner sites (Post, 1999). Defects and vacancies in the Mn-octahedra lead to alterations in surface charge, and edge sites allow for sorption and oxidation on the mineral surface (Fischel et al., 2015a;Holguera et al., 2018;Villalobos, 2015;Zhao et al., 2018). ...
... Birnessite and lithiophorite are two common layered Mn-oxides. Tunnel structure Mn-oxides, such as todorokite, can absorb water and cations into their vacant shells (Post, 1999). Surface sites can become passivated by the adsorption of other ions from external inputs or Mn after back reactions. ...
Manganese-oxides are some of the strongest oxidants and sorbents in the environment, which impact many geochemical processes. However, nearly all our understanding of manganese-oxides' reaction kinetics is based on laboratory-synthesized minerals. This study quantifies the oxidative kinetics and adsorptive capacity of five soils rich in pedogenic manganese-and iron-oxides through arsenite oxidation batch reactions over a range of pHs and temperatures to mimic diverse environmental conditions. The two A horizons were less reactive and enriched in manganese(IV), compared to the B horizons, particularly the subsoil containing the manganese-rich wad material. The reaction kinetics fit a pseudo-first-order reaction with distinct fast and slow phases. The baseline reactions were pH 7.2 at 23 • C. Adjusting pH to 4.5 or 9.0 increased the reaction rates. Decreasing the temperature to 4.0 • C reduced the reaction kinetics, while raising the temperature to 40 • C increased the arsenite oxidation rate. pH and temperature changes alter the reaction kinetics due to shifts related to the point of zero charge, the total system energy, and surface passivation from adsorbing arsenic and manganese species. Synchrotron X-ray fluorescence mapping indicates arsenic only penetrates the surficial layers of most manganese-oxide-containing nodules found in the soil. After the arsenite oxidation reaction in the pedogenically weathered subsoil, X-ray absorption spectroscopy demonstrates significant differences in the average manganese oxidation number between the nodules' outer layers compared to the soil matrix and nodule centers. The kinetic and sorption parameters give critical insight into determining the mobility and species of arsenic and other redox-sensitive contaminants in manganese-containing environmental systems over appropriate timescales.
... Identifying manganese oxide minerals poses a challenge due to their nano-crystalline nature, complex intergrowth of different phases, and structural and oxidation-state variations (Mn 2+ to Mn 7+ ) [7]. The atomic frameworks of these minerals are constructed from Mn-O octahedra that share edges and link corners to yield an array of phases with tunnel or layer structures [8,9]. ...
... The tunnel-structured Mn oxides are assembled from single, double, or even triple chains of edge-sharing MnO 6 octahedra, and the chains share corners to manufacture frameworks that consist of tunnels with square or rectangular cross-sections. In contrast, the layer-structured Mn oxides comprise stacks of sheets of edge-sharing MnO 6 octahedra [7][8][9]. ...
The present research explores the potential of manganese oxide waste ore in energy storage applications, focusing on supercapacitors. The investigation assesses the electrochemical capabilities of natural manganese oxides obtained from the Drama region, which has been the main mining center of Greece for manganese ore, especially that of battery-grade quality. Samples were collected from abandoned mining sites in the Kato Nevrokopi area, Drama. The structure and composition of the manganese minerals were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical tests involved the preparation of electrodes using natural nsutite and heat-treated nsutite (hausmannite). Then, the designed electrodes were subjected to cyclic voltammetry tests and charge-discharge measurements. The hausmannite electrode exhibited a higher specific capacitance of 667 F/g at a current density of 0.2 A/g, and the electrode material retained 98.3% of its initial capacitance after 1000 cycles. This study provides new perspectives on simple and efficient methods for transforming natural nsutite material from mining waste to hausmannite with greater structural homogeneity and better electrochemical behavior.
... Abiotic Mn(II) removal may occur via two pathways: 1) homogenous oxidation in the water phase (negligible according to [12], 2) direct adsorption of Mn(II) on the filtration media, followed by heterogeneous oxidation of sorbed Mn(II) with MnOx on the filter media coating to form new MnOx. The second mechanism is also known as autocatalytic oxidation [10,11,13,14]. However, in addition to the Mn(II) adsorption mechanism on the MnOx-coated media, there is a simultaneous heterogeneous oxidation process that continuously decreases the Mn(II) surface loading and maintains the adsorption driving force. ...
... Despite their low concentration in soils, Mn oxides are highly reactive minerals that can sorb contaminants and can also catalyze other reactions (Grangeon et al., 2020). Many Mn oxides common in soils (e.g., birnessite, todorokite, and lithiophorite) contain some Mn 3+ or Mn 2+ in their structures (in addition to mostly Mn 4+ ) which permits them to function both as an oxidant and also as a reductant as they facilitate single electron transfers (gain or loss) to/from other redox species while maintaining their solid phase (Grangeon et al., 2020;Post, 1999). Manganese oxides can catalyze reactions in soils, such as the oxidation of Cr, Co, and As and also has been reported to facilitate the oxidation of some organic contaminants (Bartlett & James, 1979;McBride, 1987). ...
Manganese (Mn) oxide‐coated sand has been suggested as an amendment for scrubbing metals in water filtration beds and also as a less concentrated medium for uniformly amending soils with Mn oxides in mesocosm scale studies. Earlier work at the lab bench scale, using potassium permanganate (KMnO4) solutions that were reduced with sodium (Na) lactate, resulted in sands coated with about 0.13% Mn. The goal of this project was to increase the amount of Mn oxide that could be coated on sand to make it a more useful amendment and also to attempt to scale up the procedure to produce larger (kg) quantities of coated sand. Titration experiments examined the effects of (1) varying the molar ratio of Na lactate to KMnO4, (2) varying the rate at which the titration was accomplished, and (3) varying the concentration (molarity) of the original KMnO4 solution. The results of this work led to an optimal approach utilizing 0.32 M KMnO4 solution that was titrated to a final lactate:permanganate ratio of ∼1.1 with 10% of the lactate being added every 10 min while the suspension was being stirred. The proportion of sand to an initial solution was also increased 5–20 fold to between 50 and 200 g per 100 mL of solution. Applying this method and using a large 20‐ to 30‐L reaction vessel yields sands coated with up to 0.7% Mn in batches 5–10 kg is size, which could be useful as an amendment in mesocosm scale studies, or as a component of treatment filter beds. The examination of various size fractions of the coated sands demonstrated that more Mn was coated on finer sand fractions, which appears to be a function of the particle surface area available for the coating of Mn oxides, and at a rate of 0.3–0.5 µg Mn mm⁻² of the particle surface.
... The rotation data indicates that PC1 reduces primarily to Mn and MnO 2 and to a lesser extent Ba. Manganese is an abundant element, is mobile in groundwater, and is easily oxidized (Post 1999). Barium (as barite, BaSO 4 ) is found within both Precambrian-and Ordovician-age geology (Di Prisco and Springer 1991), and Ba is a natural trace element in Ontario groundwaters (Colgrove 2016). ...
The Middle to Late Woodland transition in southern Ontario (ca. 500 to 1000 CE) is widely acknowledged as the time during which there were significant changes to settlement and subsistence systems, often characterized as a gradual shift from seasonally mobile foraging-based communities to increasingly maize-focused horticultural and village societies. Associated modifications in pottery design between the Middle and Late Woodland have been used for studying cultural patterns and also for inferring processes of culture change. As a contribution to the study of the Middle to Late Woodland transition, we focus on the composition of Middle and Late Woodland pottery fabrics from the Trent Valley area of south-central Ontario. Our study is based on trace elements and macro-characteristics of pottery temper, characterized using X-ray fluorescence and visual analysis. Our results show there are statistically significant changes between the two periods, including a reduction in fabric variability over time. We interpret this as reflecting a geographic narrowing of the taskscape and range of source materials used for pottery manufacture, consistent with expectations of a reduction in mobility between the two periods. We also introduce the possibility of ceramic exchange between coeval foraging and farming communities in the Trent Valley.
... Contamination occurs due to concentrations of heavy metal Mn and E. coli bacteria that exceed the quality standard for drinking water. Mn minerals are very abundant in nature, in rock layers in the form of manganese ore and ferrous manganese [POST 1999] which are then dissolved by groundwater to form brown or blackish deposits of manganese oxide. Contamination caused by rock minerals is called geogenic contamination. ...
... Manganese dioxide has properties such as strong oxidation and adsorption capacity (Post, 1999), mineral abundance (Kim et al., 2013;Zhang et al., 2014), acid resistance (Kim et al., 2013), and low toxicity (Chen et al., 2010). These unique properties make manganese dioxide a widely used material (Yadav & Xu, 2012), for example, MnO 2 finds applications in the glass and enamel industries as a coloring, decolorizing, and iron removal agent, as well as in the dry battery sector as a catalyst and oxidizing agent. ...
Liquid-phase catalytic hydrogenation is a non-polluting and highly efficient technique for the reductive removal of hexavalent chromium from water, which has the advantages of a simple device, easy operation, mild, and green reaction conditions without secondary pollution, and high efficiency. In this study, the loaded catalysts Pd/(MnO2@PANI) and Pd/MnO2 were synthesized by the precipitation deposition method, and the composition and morphology of the catalysts were analyzed by using ICP, XRD, XPS, and TEM characterization. The effects of different catalysts, catalyst dosage, initial Cr(VI) concentration, pH value, and palladium loading on the Cr(VI) reduction reaction were also investigated using Pd/(MnO2@PANI) and Pd/MnO2 as catalysts and formic acid as hydrogen source. The results showed that the reduction of 1 mM Cr(VI) was 99.4% after 120 min at pH 2 and 0.2 g/L catalyst. After 5 consecutive cycles, the reduction rate of Pd/(MnO2@PANI) remained at 41.5%, and the reduction efficiency of Pd/MnO2 was only 23.7% after five cycles, which indicated that Pd/(MnO2@PANI) with polyaniline as the coating layer is a more efficient and stable catalyst that can be recycled for the treatment of Cr(VI) in water. At the same time, after the coating of MnO2 with polyaniline, the original low toxicity and wide source of MnO2 will not affect the survival of other plants and animals and will not pollute the environment, and the use of Pd/(MnO2@PANI) for the reduction of Cr(VI) is of good practical significance, which provides a new solution for the treatment of chromium pollution.
... A correlation plot between soluble Mn with TA is shown in Fig. 8d, which displays a positive correlation and provides a hint of contribution of soluble Mn from chemical processing. Unlike Fe, Mn (as oxide) bearing common minerals like the Todorokite and Birnessite have layered crystal structure and can readily undergo oxidative reduction which make them more labile (Post, 1999). Other than Mn-oxide, Mn bearing carbonates and desert varnishes (formed by Mn-oxidizing microbes) on hard rock surface and their subsequent weathering and transport to the atmosphere can leads to high EF Mn over remote marine locations (Bullard et al., 2004;Chance et al., 2015). ...
... Also, large intracrystalline distances or defects in the crystal increase the available surface area and can act as active adsorption centers. Most naturally occurring Mn oxides are poorly crystalline with a layered structure (Post 1999). According to Weaver and Hochella (2003), the following hierarchy represents the ability of different minerals to oxidize Cr(III): birnessite > hausmannite >> romanechite > cryptomelane >> manganite > pyrolusite >> lithiophorite. ...
The chromium origin in the environment can be geogenic, anthropogenic, or both. The most common forms of chromium in soil and water are various species of Cr(III) or Cr(VI). Cr(III) has low solubility at most environmental conditions, and rarely exceeds the maximum permissible drinking water concentration, while it is an essential nutrient trace element for plant and animal metabolism. Unlike Cr(III), Cr(VI) is very soluble, strong oxidizer, unstable in the presence of reducing agents (electron donors), toxic and carcinogenic. The limit of chromium concentration in drinking water according to the International Health Organization and the EU is 50 μg/L referred as total chromium. Key parameters that determine the distribution of various chromium species in the natural environment are: the geochemical environment, pH and the redox potential (Eh). The conversion of Cr(III) to Cr(VI) is possible in alkaline and oxidizing (Eh > 0) conditions. There are a few agents in the natural environment capable of oxidizing chromium. Mn oxides (Mn(III), Mn(IV) oxy-hydroxides and Mn(IV) oxides such as pyrolusite), are the only naturally occurring minerals capable of oxidizing Cr(III) to Cr(VI). Inhibition of Cr(III) oxidation can occur due to competitive adsorption of some cations (La, Al, Mn(II)) on Mn oxide surface. Precipitation of Cr(OH)3 · nH2O and Al(OH)3 formed on Mn oxide surface can also inhibit Cr(III) oxidation. A portion of Cr(VI) formed by oxidation of Cr(III) is released back into solution while a part of it remains adsorbed on the MnOx surface and associated to the matrix. The release of hexavalent chromium into aqueous phase can be enhanced by competitive anion adsorption (e.g., phosphates) increasing hexavalent chromium concentration: phosphates directly remove chromates by competing Cr(VI) for the adsorption sites or indirectly by increasing the pH of solution. Cr(VI) is reduced in soil and water to Cr(III), in the presence of reductants such as S2−, V2+, Fe2+, HNO2, \({\text{HSO}}_{{3}}^{ - }\) and some organic species. Cr(VI) reduction in water with soil and sediment is very rapid while the reduced chromium is resistant to reoxidation. The inhibition of Cr(III) oxidation and Cr(VI) reduction can reduce the pollution caused by Cr(VI), only by natural attenuation, without any human intervention. The deeper levels of an aquifer have a clearly different water composition from the shallow levels. At greater depths the dominant form is Cr(VI), at intermediate depths the dominant form is again Cr(VI) but in lower concentrations. On the other hand, the shallow wells have Cr(III) as the dominant form, in coexistence with nitrates as a result of fertilization and increased water reflow, through the unsaturated zone during irrigation. The differences in water quality, as a function of depth, are very often due to the increased pumping.
... [9,10] With OMS naturally existing in terrestrial Mn ore deposits and marine sediments, its reversible ionic storage also balances the global tracemetal cycling in underground soil and seawater, making it the interest of (bio)geochemists. [11,12,13] Nevertheless, it is within the past two decades that OMS has gained rising attentions, thanks to the blooming of nanotechnology and sustainable energy technologies. [14,15] Specifically, the low cost, high environmental friendliness and suitable pore size make OMS a good candidate for energy storage, (electro)catalysis, ion exchange and deionization; [16,17] in addition, many laboratory-based methods (sol-gel, hydrothermal, electrodeposition, etc.) have been developed to synthesize nanosized OMS possessing large specific surface area and high physicochemical activity, further boosting the their clean energy applications. ...
Tunnel‐structured manganese dioxides (MnO2), also known as octahedral molecule sieves (OMS), are widely studied in geochemistry, deionization, energy storage and (electro)catalysis. These functionalities originate from their characteristic sub‐nanoscale tunnel framework, which, with a high degree of structural polymorphism and rich surface chemistry, can reversibly absorb and transport various ions. An intensive understanding of their structure–property relationship is prerequisite for functionality optimization, which has been recently approached by implementation of advanced (in situ) characterizations providing significant atomistic sciences. This review will thus timely cover recent advancements related to OMS and their energy storage applications, with a focus on the atomistic insights pioneered by researchers including our group: the origins of structural polymorphism and heterogeneity, the evolution of faceted OMS crystals and its effect on electrocatalysis, the ion transport/storage properties and their implication for processing OMS. These studies represent a clear rational behind recent endeavors investigating the historically applied OMS materials, the summary of which is expected to deepen the scientific understandings and guide material engineering for functionality control.
... [9,10] With OMS naturally existing in terrestrial Mn ore deposits and marine sediments, its reversible ionic storage also balances the global tracemetal cycling in underground soil and seawater, making it the interest of (bio)geochemists. [11,12,13] Nevertheless, it is within the past two decades that OMS has gained rising attentions, thanks to the blooming of nanotechnology and sustainable energy technologies. [14,15] Specifically, the low cost, high environmental friendliness and suitable pore size make OMS a good candidate for energy storage, (electro)catalysis, ion exchange and deionization; [16,17] in addition, many laboratory-based methods (sol-gel, hydrothermal, electrodeposition, etc.) have been developed to synthesize nanosized OMS possessing large specific surface area and high physicochemical activity, further boosting the their clean energy applications. ...
Tunnel‐structured manganese dioxides (MnO2), also known as octahedral molecule sieves (OMS), are widely studied in fields of geochemistry, deionization, energy storage and (electro)catalysis. These functionalities originate from their characteristic sub‐nanoscale (Å‐scale) tunnel framework, which, with a high degree of structural polymorphism and rich surface chemistry, can reversibly absorb and transport various cationic species. Therefore, an intensive understanding of structure‐property relationship, especially down to the sub‐nanoscale tunnel dimension, is prerequisite for functionality optimization. This goal has been recently approached by implementation of advanced (in situ) characterizations providing significant atomistic sciences. This review will thus timely cover recent advancements related to OMS materials and their energy storage applications, with a focus on the atomistic insights into the structure‐property relationship pioneered by researchers including our group: the origins of structural polymorphism and heterogeneity, the evolution of faceted OMS crystals and its effect on surface‐sensitive electrocatalysis, the ion transport/storage behaviors within OMS tunnels and their implication for performance‐enhancement strategies. These essentially consistent studies represent a clear rational behind the recent research endeavors exploring the fundamentals of the historically applied OMS materials, the summary of which is expected to highlight the importance of obtaining microscopic structure‐property relationship of functional materials for material design guidance.
Mn(II)-oxidizing microorganisms are considered to play significant roles in the natural geochemical cycles of Mn and other heavy metals because the insoluble biogenic Mn oxides (BMOs) that are produced by these microorganisms adsorb other dissolved heavy metals and immobilize them as precipitates. In the present study, a new Mn(II)-oxidizing fungal strain belonging to the ascomycete genus Periconia, a well-studied plant-associating fungal genus with Mn(II)-oxidizing activity that has not yet been examined in detail, was isolated from natural groundwater outflow sediment. This isolate, named strain TS-2, was confirmed to oxidize dissolved Mn(II) and produce insoluble BMOs that formed characteristic, separately-located nodules on their hyphae while leaving major areas of the hyphae free from encrustation. These BMO nodules also adsorbed and immobilized dissolved Cu(II), a model analyte of heavy metals, as evidenced by elemental mapping analyses of fungal hyphae-BMO assemblages using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX). Analyses of functional genes within the whole genome of strain TS-2 further revealed the presence of multiple genes predicted to encode laccases/multicopper oxidases that were potentially responsible for Mn(II) oxidation by this strain. The formation of BMO nodules may have functioned to prevent the complete encrustation of fungal hyphae, thereby enabling the control of heavy metal concentrations in their local microenvironments while maintaining hyphal functionality. The present results will expand our knowledge of the physiological and morphological traits of Mn(II)-oxidizing Periconia, which may affect the natural cycle of heavy metals through their immobilization.
The abiotic transformations of quinolones and tetracyclines facilitated by redox-active minerals has been studied extensively, however limited information is available regarding the antimicrobial activity and toxicity of their resultant transformation products. In this study, we first investigated the mechanisms underlying the transformation of two commonly used antibiotics, ciprofloxacin (CIP) and tetracycline (TC), by the ubiquitous redox soil mineral, birnessite (MnO2). Subsequently, we evaluated the impact of these transformation products on both the growth and activity of the environmental denitrifier Pseudomonas veronii. Following the reaction with birnessite, four transformation products for CIP and five for TC were identified. Remarkably, the antibacterial activity of both CIP and TC was lost upon the formation of transformation products during their interaction with birnessite. This loss of antimicrobial efficacy was associated with specific chemical transformations, such as the opening of the piperazine ring for CIP and hydroxylation and demethylation for TC. Interestingly, denitrifying activity, quantified in terms of nitrate reduction rates, remained unaffected by both CIP and TC at low concentrations that did not impact bacterial growth. However, under certain conditions, specifically at low concentrations of CIP, the second step of denitrification—nitrite reduction—was hindered, leading to the accumulation of nitrite. Our findings highlight that the transformation products induced by the mineral-mediated reactions of CIP or TC lose the initial antibacterial activity observed in the parent compounds. This research contributes valuable insights into the intricate interplay between antibiotics, redox-active minerals, and microbial activity in environmental systems.
Using different prebiotically plausible activating reagents, the RNA ligation yield was significantly increased in the presence of Mn(II). The mechanism of the activation reaction has been investigated using 5'-AMP as...
Soils play a dominant role in supporting the survival and growth of crops and they are also extremely important for human health and food safety. At present, the contamination of soil by heavy metals remains a globally concerning environmental issue that needs to be resolved. In the environment, iron plaque, naturally occurring on the root surface of wetland plants, is found to be equipped with an excellent ability at blocking the migration of heavy metals from soils to plants, which can be further developed as an environmentally friendly strategy for soil remediation to ensure food security. Because of its large surface-to-volume porous structure, iron plaque exhibits high binding affinity to heavy metals. Moreover, iron plaque can be seen as a reservoir to store nutrients to support the growth of plants. In this review, the formation process of iron plaque, the ecological role that iron plaque plays in the environment and the interaction between iron plaque, plants and microbes, are summarized.
The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions (birA) to complete dehydration, and the involved mechanisms were scrutinized. Density Functional Theory (DFT) simulations were employed to derive structural models for lamellar A0.33MnO2·xH2O (A = Na+ or K+, x = 0 or 0.66), subsequently compared with the experimental results obtained for Na0.30MnO2·0.75H2O and K0.22MnO2·0.77H2O materials. Thermal analysis (TGA-DSC), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Near Ambient Pressure X-ray Photoemission Spectroscopy (NAP-XPS) measurements were conducted for both birnessites. Dehydration under vacuum, annealing, or controlled relative humidity were considered. Results indicated that complete birnessite dehydration was a two-stage process. In the first stage, water removal from the interlayer of fully hydrated birnessite (birA) down to a molar H2O/A ratio of ∼2 (birB) led to the progressive shrinkage of the interlayer distance (3% for Na birnessite, 1% for K birnessite). In the second stage, water-free (birC) domains with a shorter interlayer distance (20% for Na birnessite, 10% for K birnessite) appeared and coexisted with birB domains. Then, birB was essentially transformed into birC when complete dehydration was achieved. The vibrational properties of birA were consistent with strong intermolecular interactions among water molecules, whereas partially dehydrated birnessite (birB) showed a distinct feature, with 3 (for Na-bir) and 2 (for K-bir) vibrations that were reproduced by DFT calculations for organized water into the interlayer (x = 0.66). The study also demonstrated that the electronic structure of Na birnessite depends on the interlayer water content. The external Na+ electronic level (Na 2p) was slightly destabilized (+0.3 eV binding energy) under near ambient conditions (birA) compared to drier conditions (birB and birC).
It has been observed by many authors that highly active electrocatalysts are frequently “disordered” or “amorphous” in nature. The correlation between this lack of order and functionality is highly debated, with researchers still questioning if this structural property is a simple coincidence of the material preparation method, or if this lack of order has an important functional role for these catalysts. Using metal oxides as an example, how amorphous and disordered metal oxides can react by fundamentally different pathways are explored from more ordered forms with very similar bonding and redox states. The distinction between amorphous, disordered, and crystalline materials is reviewed in different characterization methods and suggests how these material characteristics fundamentally change the reactivity of these materials beyond surface area effects. How disorder can change the underlying thermodynamic stability of a material is explored, which in turn impacts redox potential, proton‐transfer, and electron‐transfer properties. It is these fundamental properties that govern the electrocatalytic activity and microbial metabolism of these materials. It is further argued that understanding the amorphous and disordered state of materials may be key to understanding a range of catalytic reactions; from clean energy reactions to the biological systems that underpin life's existence.
Manganese-based (Mn-based) nanomaterials (NMs) have great potential as alternatives to conventional Mn fertilizers. Yet, its environmental risks and effects on plant growth are not completely well understood. This study investigated the physiological effects of manganese dioxide (MnO2) and manganese tetroxide (Mn3O4) NMs on inter-root exposure (0–500 mg/L) of hydroponically grown rice. The results showed that on inter-root exposure, 50 mg/L Mn-based NMs promoted the uptake of mineral elements and enhanced the enzymatic activities of antioxidant systems (CAT and SOD) in rice, whereas 500 mg/L Mn3O4 NMs disrupted the mineral element homeostasis and led to phytotoxicity. The promotion effect of MnO2 NMs was better, firstly because MnO2 NMs treatment had lower Mn content in the plant than Mn3O4 NMs. In addition, MnO2 NMs are more transported and absorbed in the plant in ionic form, while Mn3O4 NMs exist in granular form. MnO2 NMs and Mn3O4 NMs both can be used as nano-fertilizers to improve the growth of rice by inter-root application, but the doses should be carefully selected.
Graphical Abstract
This research presents an analysis of physico-chemical, structural and electrochemical properties of cathode materials for aqueous zinc-ion batteries based on manganese dioxide with birnessite-type structure in dependence on the conditions of hydrothermal synthesis. The manganese oxides obtained are capable to the reversible zin ions intercalation into the crystal lattice because of large interlayer distances. They were considered two approaches of synthesis: a reaction between manganese sulfate and potassium permanganate at 160 °С (MnO2-I) and a hydrothermal treatment of potassium permanganate solution at 220 °С (MnO2-II). From the structural analysis it was shown that both methods allow obtaining the birnessite-type manganese dioxide. At the same time, electrochemical properties of cathodes obtained differ in the models of aqueous zinc-ion batteries. MnO2-II material demonstrate higher initial specific capacity (180 mAh∙g-1 at current density 0.3 A∙g-1) while its cyclic stability is on 40% lower than for MnO2-I material. This can be explained with higher surface area of the active material and lower crystallinity.
Developing highly active and durable catalysts in acid conditions remains an urgent issue due to the sluggish kinetics of oxygen evolution reaction (OER). Although RuO 2 has been a state‐of‐the‐art commercial catalyst for OER, it encounters poor stability and high cost. In this study, the electronic reservoir regulation strategy is proposed to promote the performance of acidic water oxidation via constructing a RuO 2 /MnO 2 heterostructure supported on carbon cloth (CC) (abbreviated as RuO 2 /MnO 2 /CC). Theoretical and experimental results reveal that MnO 2 acts as an electron reservoir for RuO 2 . It facilitates electron transfer from RuO 2 , enhancing its activity prior to OER, and donates electrons to RuO 2 , improving its stability after OER. Consequently, RuO 2 /MnO 2 /CC exhibits better performance compared to commercial RuO 2 , with an ultrasmall overpotential of 189 mV at 10 mA cm ⁻² and no signs of deactivation even after 800 h of electrolysis in 0.5 m H 2 SO 4 at 10 mA cm ⁻² . When applied as the anode in a proton exchange membrane water electrolyzer, the cost‐efficient RuO 2 /MnO 2 /CC catalyst only requires a cell voltage of 1.661 V to achieve the water‐splitting current of 1 A cm ⁻² , and the noble metal cost is as low as US$ 0.00962 cm ⁻² , indicating potential for practical applications.
Manganese is one of the most prevalent elements in the earth’s crust, deposited in the form of different oxides. Strategically, it is an important metal that has augmented industrial applications. Being a cofactor of multiple metabolic enzymes, the Mn (II) ion exhibits a crucial role as an essential trace element of all living organisms. Rapid industrialization, mining, mineral processing, and further anthropogenic activities imposed severe consequences on the generation of a large amount of manganese mining waste product. The inappropriate supervision and unprocessed dumping of these Mn waste products have caused a significant threat to the ecosystem and public health. Hence, remediation is required to avoid heavy metal mobilization into environmental segments and facilitate their extraction. At first, this chapter introduces the essentiality, toxicity, and regulation of Mn. Various Mn-solubilizing microorganisms mediated In-situ approaches to bioremediation, viz., microbially induced carbonate precipitation (MICP), biomineralization, biosorption, bioaccumulation, bio-oxidation, bioleaching, biomining, bioventing, disparaging, biostimulation, and bioaugmentation, are discussed in detail. To promote bioremediation efficiency, the combination of different techniques is preferred. Finally, we propose the cost-efficient and eco-friendly future approach of Mn bioremediation without producing any secondary pollutants and, conclusively, providing a scientific basis for the microbial remediation performance for Mn pollution.
Apart from our imagination, the nanotechnology industry is rapidly growing and promises that the substantial changes that will have significant economic and scientific impacts be applicable to a wide range of areas, such as aerospace engineering, nanoelectronics, environmental remediation, and medical healthcare. In the medical field, magnetic materials play vital roles such as magnetic resonance imaging (MRI), hyperthermia, and magnetic drug delivery. Among them, manganese oxide garnered great interest in biomedical applications due to its different oxidation states (Mn2+, Mn3+, and Mn4+). Manganese oxide nanostructures are widely explored for medical applications due to their availability, diverse morphologies, and tunable magnetic properties. In this review, cogent contributions of manganese oxides in medical applications are summarized. The crystalline structure and oxidation states of Mn oxides are highlighted. The synthesis approaches of Mn-based nanoparticles are outlined. The important medical applications of manganese-based nanoparticles like magnetic hyperthermia, MRI, and drug delivery are summarized. This review is conducted to cover the future impact of MnOx in diagnostic and therapeutic applications.
The increasing intensity of human activities has led to a critical environmental challenge: widespread metal pollution. Manganese (Mn) oxides have emerged as potentially natural scavengers that perform crucial functions in the biogeochemical cycling of metal elements. Prior reviews have focused on the synthesis, characterization, and adsorption kinetics of Mn oxides, along with the transformation pathways of specific layered Mn oxides. This review conducts a meticulous investigation of the molecular-level adsorption and oxidation mechanisms of Mn oxides on hazardous metals, including adsorption patterns, coordination, adsorption sites, and redox processes. We also provide a comprehensive discussion of both internal factors (surface area, crystallinity, octahedral vacancy content in Mn oxides, and reactant concentration) and external factors (pH, presence of doped or pre-adsorbed metal ions) affecting the adsorption/oxidation of metals by Mn oxides. Additionally, we identify existing gaps in understanding these mechanisms and suggest avenues for future research. Our goal is to enhance knowledge of Mn oxides' regulatory roles in metal element translocation and transformation at the microstructure level, offering a framework for developing effective metal adsorbents and pollution control strategies.
In the context of growing arsenic (As) contamination in the world, there is an urgent need for an effective treat-
ment approach to remove As from the environment. Industrial wastewater is one of the primary sources of As
contamination, which poses significant risks to both microorganisms and human health, as the presence of As can
disrupt the vital processes and synthesis of crucial macromolecules in living organisms. The global apprehension
regarding As presence in aquatic environments persists as a key environmental issue. This review summarizes the
recent advances and progress in the design, strategy, and synthesis method of various manganese-based adsor-
bent materials for As removal. Occurrence, removal, oxidation mechanism of As(III), As adsorption on man-
ganese oxide (MnOx)-based materials, and influence of co-existing solutes are also discussed. Furthermore, the
existing knowledge gaps of MnOx-based adsorbent materials and future research directions are proposed. This re-
view provides a reference for the application of MnOx-based adsorbent materials to As removal.
Ferromanganese (Fe-Mn) polymetallic nodules are significant marine mineral resources containing various metal elements of substantial economic and scientific research value. Previous studies have primarily focused on the mineralogy and geochemistry of the nodules, while research on their nano-mineralogy is still lacking. In this study, we conducted scanning electron microscopy (SEM), X-Ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) porous structure gas adsorption/desorption, and specific surface area analysis to examine the nano-mineralogy and mineralization of the polymetallic nodules from the interbasin of seamounts in the western Pacific Ocean (IBSWP). The results indicate that the growth profiles of the IBSWP polymetallic nodules exhibit microstructural features such as laminated, stromatolithic, columnar, and mottled structures. The mineral compositions are primarily composed of Fe-Mn minerals and detritus, including quartz; minerals from the feldspar group; and minerals from the clay group. The Fe-Mn phase minerals are relatively poorly crystallized. The Mn-phase minerals contain vernadite and small amounts of todorokite, buserite, and birnessite, while the Fe-phase minerals are mainly comprised of amorphous FeOOH. The main ore-forming minerals consist of nano-minerals, and the nanostructures of the polymetallic nodules endow them with unusually large specific surface areas and pore volumes, resulting in strong adsorption properties. The unique nano-properties and surface/interface adsorption effects of Fe-Mn minerals play a crucial role in controlling the enrichment of ore-forming elements.
The main structural building blocks that form manganese oxides are MnO 6 octahedra; these share corners and edges to construct specific structures, which can either be tunneled or layered. In the layered structures, that is, phyllomanganates, the MnO 6 octahedra form sheets, which, in turn, alternate with sheets of metal oxides and H 2 O. These metal ions can vary (Zn, Co, Ni, Al, Li, …) and give rise to an entire range of different metal oxides. The characterization of these layered materials is important as they have various economical/industrial applications. Birnessite‐type materials, a specific type of layered manganese oxides, are widely studied for their use as cathode materials in alkali‐ion batteries. Phyllomanganates are also commonly found as constituents in sediments and soils or as coatings on rock surfaces. Their natural occurrence as black colored components have ensured that these minerals were also applied as pigments in archaeological and historical contexts. They are, for example, often found in rock art paintings and on pottery. As the oxides are used in unique archaeological objects, Raman spectroscopy is an evident choice for characterization due to its non‐destructive nature of analysis. In the current study, five mineral samples of (layered) manganese oxides are analyzed with different Raman instrumentations, including mobile systems and a benchtop micro‐Raman setup. The characterization of each selected manganese oxide and their comparison with literature data is discussed for the micro‐Raman instrumentation. In addition, the ability of identifying and characterizing layered manganese oxides and the possible challenges when using mobile instrumentation are discussed as well.
Atomically thin, few‐layered membranes of oxides show unique physical and chemical properties compared to their bulk forms. Manganese oxide (Mn3O4) membranes are exfoliated from the naturally occurring mineral Hausmannite and used to make flexible, high‐performance nanogenerators (NGs). An enhanced power density in the membrane NG is observed with the best‐performing device showing a power density of 7.99 mW m⁻² compared to 1.04 µW m⁻² in bulk Mn3O4. A sensitivity of 108 mV kPa⁻¹ for applied forces <10 N in the membrane NG is observed. The improved performance of these NGs is attributed to enhanced flexoelectric response in a few layers of Mn3O4. Using first‐principles calculations, the flexoelectric coefficients of monolayer and bilayer Mn3O4 are found to be 50–100 times larger than other 2D transition metal dichalcogenides (TMDCs). Using a model based on classical beam theory, an increasing activation of the bending mode with decreasing thickness of the oxide membranes is observed, which in turn leads to a large flexoelectric response. As a proof‐of‐concept, flexible NGs using exfoliated Mn3O4 membranes are made and used in self‐powered paper‐based devices. This research paves the way for the exploration of few‐layered membranes of other centrosymmetric oxides for application as energy harvesters.
Metal (oxyhydr)oxides are key factors for the transformation and stabilization of organic carbon (OC) in soil. While sorptive interactions between Al and Fe (oxyhydr)oxides and dissolved organic matter (DOM) are well studied, the role of Mn(IV) oxides (manganates) in DOM sorption, fractionation, and oxidation has not been extensively investigated. Therefore, we examined sorptive interactions between manganates (δ-MnO2, birnessite, cryptomelane; 5 g L-1) and different DOM types (beech litter and Oa/Oe material under pine; ~100 mg L-1 dissolved organic carbon, DOC) at pH 4 and 7 in different background electrolytes (BGE; no salt, 0.01 M NaCl or CaCl2) for up to 32 hours. Changes of DOM solutions and mineral phases were assessed by solid, liquid, and gas analyses, and statistically evaluated for the effects of manganate, DOM type, pH, and BGE on DOC sorption, fractionation, and oxidative transformation. Manganates sorbed 0.2–8.7 mg OC g-1. Per unit mass, δ-MnO2 was least effective in DOC retention due to its high DOC oxidation capacity. Manganates sorbed more DOC at acidic pH and more aromatic pine than more aliphatic beech DOC, with Ca2+ generally facili-tating DOC sorption. Up to 56 % of added DOC (average: 25 %) was oxidized to CO2, which is comparable to the extent of DOC respiration by soil microorganisms. DOC oxidation by δ-MnO2 and cryptomelane exceeded that of birnessite, which had the lowest specific surface area of all manganates. However, we found no difference in the efficiency of manganates to oxidize DOC, implying a similar redox activity of phyllo- and tectomanganates. More beech than pine DOM was oxidized to CO2 and an acidic pH facilitated DOC decomposition. While the presence of Na-BGE increased DOC oxidation to CO2 relative to no-salt treatments, Ca-BGE had the opposite effect, as Ca2+ apparently impeded the electron transfer from sorbed OC to structural Mn(III/IV). Contact of DOM with manganates also produced high concentrations of dissolved low-molecular-weight organic acids (mainly formate, acetate, and oxalate), accounting for up to 19 % of the initial DOC concentration. In addition, reduced specific ultraviolet absorbance of DOM solutions at 280 nm indicated preferential sorption of aromatic moieties, especially in Ca-BGE. However, in the absence of Ca2+ and at neutral pH, manganates increased the aromaticity of beech DOM, most likely due to polymerization reactions. No mineral transformations occurred after reaction of manganates with DOM, despite reductive manganate dissolution. Our results imply that soil manganates accumulate more OC in acidic soils and in presence of more aromatic DOM. However, manganates oxidatively destabilize DOC by generating CO2 and low-molecular-weight organic compounds, which is presumably more relevant in acidic soils with low concentrations of polyvalent cations and for more aliphatic DOM. The produced low-molecular-weight organic compounds may promote microbial activity and foster mineral weathering. Our results suggest a pivotal role of manganates in soil OC cycling, including the fate and bioavailability of nutrient elements associated with DOM, and in supporting ligand-promoted mineral weathering and soil formation.
A sodium-bearing manganese oxide hydrate is reported from shallow-water Fe-Mn crusts of the Manus Island region, SW Pacific. On the basis of its transformation on heating to 100oC, its chemistry and its intercalation with dodecylammonium ions, this mineral is considered to be a natural buserite (Na4Mn14O27.21H2O) (A.M. 68-972, 70-205). The structural changes under heating and intercalation indicate that the mineral is buserite I (in the classification of Chukhrov et al. (M.A. 87M/3124)), and the presence of Mg supports the hypothesis that Mg replacement influences stability. Techniques for distinction between buserite and todorokite are discussed. -R.A.H.
Ernienickelite is a new mineral species in the chalcophanite group from the SM7 pit, Siberia ultramafic complex, Western Australia, Australia. It occurs in a Ni-Co laterite as a rare constituent in cavities of quartz (chalcedony) associated with goethite, magnesite, a serpentine-group mineral, nimite and nontronite. The physical, optical and crystallographic properties of ernienickelite are described. The crystal structures of ernienickelite and chalcophanite are compared to those of lithiophorite and cianciulliite. The X-ray powder-diffraction data for chalcophanite and aurorite are corrected, refined and indexed. -from Authors
A synthetic phyllomanganate saturated with a series of primary alkylammonium cations has been examined using XRD, chemical analysis and X-ray photoelectron spectroscopy. A linear relationship exists between the basal spacing of the saturated alkylammonium-manganate and the hydrocarbon chain length in the interlayer, and from the gradient it is concluded that the alkyl chains are perpendicular to the manganate sheet. This orientation is a function of both the charge density and the presence of a layer of water molecules immediately adjacent to the manganate basal surfaces. Evacuation results in the loss of this interlayer water and the structure of the organo-manganate is considerably disrupted. The extent to which the interlayer arrangement can be re-instated by rehydration is dependent on the chain length of the saturating organo-cation. For cations of chain length >C6 the C contents suggest that cation in excess of the exchange capacity is present in the interlayer, but the absence of any compensating anion and the release of amine on evacuation suggests that the excess C arises from the presence of free amine. (Authors' abstract)-D.J.M.
Manganese ores were known to mankind since the ancient times irrespective of the fact that they were often confused with iron and magnesium ores. Particularly widely known were ore minerals such as pyrolusite, that was described for the first time by Plinium as the variety of the iron magnetic oxide (magnetic iron ore or Lapis magnes). The reputation of pyrolusite can be associated with that the fact that remarkably it removes the green tint, imparted by iron oxides to even light varieties of glass, that are the usual mixtures of the quartz sands. Plinium explained the origin of the word magnes, attributing it to the name of a legendary herdsman Magnes, who paid attention to the fact that the iron nails of his boots and the tip of his stick were pulled to the ground in those places where magnetic iron ore deposits were located (Sully, 1955), but there are many other versions in the literature. In manuscripts of the XIVth century, kept in the British Museum, such ‘new’ terms are used to designate different matters such as magnesia ferrea and magnesia, and the latter was used as an additive for the production of violet glass. Probably, this terminological ambuigity led to the fact that in manuscripts of the medieval investigator Albertus Magnus (1193–1280) there was the term manganesis, that approximates closely to the modern word by its spelling and semantic meaning. But the particular term ‘manganese’ was used in the work by V. Biringuccio (Biringuccio, 1540, cited by Sully, 1955), who indicated in 1540, that the mineral of this name occurred in Germany near the settlement Witerbo, Tusconia, as ferrous ‘cinder’, from which unlike the iron oxides it was impossible to produce metal during smelting, and that the sublimation was observed during the heating process, and this mineral turned to cinder after the vapor separation.
Todorokite is recognized as a valid mineral species. Previous comparisons of todorokite and psilomelane (romanechite) are criticized. Lattice imaging in hollandite, psilomelane and todorokite is discussed. (A.M. 68-972, 70-205)-J.A.Z.
Manganese ore (pyrolusite) and iron ore (haematite), both raw and chemically treated with ferric hydroxide, alum, lime, or manganese dioxide, were subjected to batch sorption and downflow column tests to assess their capacity to remove Escherichia coli and clay turbidity from water. Lime or alum-treated manganese ore appeared to be a promising medium for use in low-cost household water filters. In filtration of a polluted canal water heterotrophic bacteria concentrations were reduced from 400-1000 CFU/mL to 1-4 CFU/mL, E.coli from 100-400 CFU/mL to zero CFU/mL, and turbidity from 30-40 NTU to 2.5 NTU
Manjiroite, a new manganese dioxide mineral, occurs in the oxidation zone of rhodonite-tephroite-rhodochrosite bedded ore deposits of Kohare Mine, Iwate Prefecture, Japan, running along the boundaries between chert and schalstein of Permian age. It is associated with pyrolusite, nsutite, birnessite, cryptomelane and goethite. Manjiroite is dense compact masses up to 10×8×5cm., with marked conchoidal fracture. Colour dark brownish-gray, luster dull, streak brownish-black. No cleavage, sp. gr. 4.29, Vickers hardness 181 av. Under the microscope opaque, distinctly anisotropic with weak pleochroism. Analysis gives MnO2 85.79, MnO 3.17, CuO 0.03, CoO none, ZnO 0.03, MgO 0.18, CaO 0.22, Na2O 2.99, K2O 1.39, BaO 0.16, Al2O3 0.62, Fe2O3 0.40, TiO2 none, SiO2 0.12, H2O- 0.68, H2O+3.92, sum 99.71%. This corresponds to (Na0.73 K0.22 Ca0.03 Ba0.01) 0.99 (Mn4+7.46 Mn2+0.34 A10.09 Fe0.04 Mg 0.03) 7.96 O16⋅1.64H2O or (Na, K) Mn4+8 O16⋅nH2O (probably n<2). The DTA curve shows endothermal effects at 530°, 905°, and 980°C. X-ray study shows it to be tetragonal, aO 9.916, cO 2.864A, isostructural with cryptomelane. There is probably an isomorphous series between cryptomelane and majiroite. The strongest lines of the X-ray pattern are 2.406 (100) (121), 7.02 (98) (110), 3.14 (92) (130), 4.94 (77) (200), 2.160 (69) (301), 1.839 (46) (141), 1.548 (46) (251), 2.332 (38) (330), 1.431 (38) (002). The name is given in honour of Dr. Manjiro Watanabe, mineralogist, economic geologist and Emeritus Professor of Tohoku University, Japan. The mineral, Manjiroite, has been approved by the Commission on New Mineral and Mineral-Name, I. M. A.
The positions of the oxygen ions of tetragonal Mn3O4 are determined through the Debey-Scherrer X-ray analysis, by the extension of the Bertaut's method and with least square method. The assigned correction for the anomalous scattering on Mn to Fe-Ka radiation is somewhat larger than the calculated value. The two oxygen parameters ε and δ for the space-group D194n are 0.032-0.036 and 0.008-0.010. These values correspond to the case that the tetragonal deformation comes from the octahedral sites but the tetrahedral sites resist to the deformation.
The transformation of manganite during heating has been studied by single crystal X-ray diffraction methods. It is observed that manganite trans-forms into pyrolusite keeping its original axial directions parallel to those of the transformed phase. Pyrolusite then transforms into Mn203 with its [001] II [110] or [I00] ofMn2Oa; [100] !l [110] or [010] ofMn~O a and [010] !f [001] ofMn20 a. Evidence of an intermediate product in the pyrolusite --> Mn20 a reaction has been found. IKE iron, manganese forms a series of oxides and oxyhydrides, of which manganite differs from its iron analogues in that during heat treatment it transforms into MnO 2 (pyrolusite). The structure of manganite is unlike those of any iron oxyhydroxides, and iron does not form a compound similar to Mn02. Moreover MnO2, when further heated, transforms into Mn20 s (cubic), which in turn transforms into Mn304 (tetragonal) ; neither Mn203 nor Mn304 is structurally similar to cubic F%O 3 or F%O 4. Manganite occurs in mineral veins, commonly associated with baryte, calcite, chalybite, braunite, hausmannite, &c. More commonly, it occurs as a replacement of other deposits formed by meteoric waters, associated with such minerals as pyrolusite, goethite, and psilomelane. The mineral reported as manganite from Indian ore deposits in Madhya Pradesh and Goa has physical properties very similar to those of manganite, but chemical analyses show it to be near pyrolusite, and Fermor (1909) preferred the name pseudomanganite. Manganite alters very easily to pyrolusite, and perfect pseudomorphs after crystals of manganite are common. It was formerly supposed to be orthorhombic (Garrido, 1935), but Buerger (1936) showed that the diffraction symmetry was 2/m and the crystal system monoclinic with a 8.86 A, b 5-24 dr, c 5-70 _~, fi 90 ~ with 8MnO. OH in the unit cell. Pyrolusite (MnO~), on the other hand, is one of the most commonly occurring manganese minerals and is formed under oxidizing conditions.
Based on accurate X-ray diffraction intensity data collected from spherically shaped single crystals, net atomic charges and electron density distributions have been studied for MnO, Mn2SiO4, Mg2Si2O6, LiAlSi2O6 and CaMgSi2O6. Examination of various procedures for determining atomic charges in a given structure has led to the conclusion that the following approach appears to be most reliable. (1) For cations: the number of electrons in the sphere of radius ER, effective distribution radius, which is defined according to the characteristics of radial distribution functions or difference-Fourier maps, is calculated. (2) For oxygen atoms: with the cation charges fixed at the values obtained from the above procedure and the total charge of the crystal constrained to be neutral, oxygen charges are estimated from least-squares refinements using atomic scattering factors. The final charges of atoms examined are less ionic than the corresponding formal ones: those of Li, O, Mg, Al, Si, Ca and Mn are respectively + 0.7 (1), -1.1 to -1.5, + 1.4 (1) to + 1.8, + 2.4(1), + 2.2 (1) to + 2.6, + 1.4 (2) and + 1.2 (1) to + 1.6 e. Residual electron densities between Si and O have been clearly observed in difference-Fourier maps after charge refinements for crystals of LiAlSi2O6, CaMgSi2O6 and Mg2Si2O6.
An asymmetric tectonic fabric was delineated by narrow-beam bathymetric profiles in a 180-km2 area of the Mid-Atlantic Ridge crest at lat 26°N. Features of the tectonic fabric are a continuous rift valley offset by small (<10-km) transform faults and minor fracture zones expressed as valleys with intervening ridges that trend normal and oblique to the two sides of the rift valley. The discharge zone of a postulated sub-sea-floor hydrothermal convection system is focused by faults on the southeast wall of the rift valley and driven by intrusive heat sources beneath the rift valley. The rift valley has a double structure consisting of linear segments, bounded by ridges, and basins at the intersections of the minor fracture zones. The double structure of the rift valley acts like a template that programs the reproduction of the tectonic fabric. The minor fracture zones form an asymmetric V about the rift valley at variance with the symmetric small circles formed by major fracture zones. To reconcile the asymmetry of minor fracture zones with the symmetry of major fracture zones, it is proposed that the minor fracture zones have been preferentially reoriented by an external stress field attributed to interplate and intraplate motions. Major fracture zones remain symmetric under the same stress field owing to differential stability between minor and major structures of oceanic lithosphere.
We have studied the strength, stability and direction of natural remanent magnetization of 25 deep-sea, JOIDES, shallow marine and fresh-water ferromanganese nodules. The nodules contain a reasonably stable and isotropic NRM of about the same magnitude as deep-sea sediments. The recording of magnetic reversals in four of the seven large deep-sea nodules supports the slow overall growth rates measured by radioactive techniques on deep-sea nodules. In contrast with the reversed layers found in some of the deep-sea samples, all three shallow marine nodules less than 15 000 yr old have magnetic inclinations which appear parallel to the Earth's present field.
Data on the distribution of manganese nodules in sediment cores from the Pacific Ocean show that nodules in the upper 2·5 m of sediment, excluding surface nodules, are approximately equal in number to those found at the sediment surface. The vertical distribution of the buried nodules is found to be fairly regular and various theories which could account for this are mentioned.
The reduction of nitric oxide with ammonia was studied by use of deep sea manganese nodules as the catalyst. Temperatures in the range of 200–300°C were used. The initial concentrations of nitric oxide and ammonia were in the range of 500–1500 ppm and 500–1800 ppm, respectively. Total flow rates varied from 200 to 450 1.h−1, with helium as the carrier gas. An empirical rate expression was developed. The manganese nodules were found to be as effective as some commercial catalysts in the NO-NH3 reaction.
Analysis of the diffuse x-ray scattering in the one-dimensional ionic conductor K1.54-Mg0.77 Ti7.23 O16 (hollandite) yields a detailed microscopic picture of the cationic shortrange order. This order is characterized by large shifts of some ions off their crystallographic sites, evidencing that in a superionic conductor the ion-ion interaction may be stronger than the periodic potential of the host crystal.
Profiles of total suspended matter, dissolved 238U, and dissolved and particulate 234Th were determined at three stations in the Black Sea during the R.V. Knorr cruise in June 1988. Sediment traps were deployed on a free-floating mooring line to measure vertical fluxes of total mass and 234Th at two deep stations. This paper presents the first data set of 234Th/238U disequilibria in anoxic environments. Our dissolved238U results are consistent with literature data. The dissolved 238U deviates from the predicted conservative mixing activities below the depth of oxygen depletion. Dissolved 234Th deviates from secular equilibrium activities in the euphotic and suboxic zones. The profiles of dissolved 234Th across the oxic-anoxic interface are similar to those of phosphate, indicating the importance of Fe-Mn oxyhydroxides in controlling the thorium distributions. Particulate 234Th is enriched in the euphotic zone and in the upper layer of the suboxic zone. Comparison of the profiles of 234Th, Fe and Mn suggests that the distribution of 234Th is mainly controlled by the Mn rather than the Fe redox cycle. In general, BS3-2 (western basin) has higher total mass and 234Th fluxes than BS3-6 (central basin). The fluxes of 234Th measured by sediment traps deployed at depths from 40 to 150 m, range from 200 to 800 dpm m2 day−1, with a maximum at 60 m. The residence times of dissolved and particulate 234Th and total suspended materials are calculated using the irreversible scavenging model and the sediment trap flux data. The results suggest that, under these conditions, Th is a good tracer for the total mass flux.
Crystal structure determinations are reported for a) a hollandite, (Ba0.75Pb0.16Na0.10K0.04)(Mn,Fe,Al)8(O,OH)16, from Stuor Njuoskes, Sweden, with a 10.026(3), b 2.8782(7), c 9.729(3) A, beta 91.03(2)o, space group I2/m; b) a cryptomelane, (K0.94Na0.25Sr0.13Ba0.10)(Mn,Fe,-Al)8(O,OH)16, from Chindwara, India, with a 9.956(3), b 2.8705(9), c 9.706(4) A, beta 90.95(3) o, space group I2/m; c) a priderite, (K0.90Ba0.35)(Ti,Fe,Mg)8O16, from the West Kimberley area, Western Australia, with a 10.139(2), c 2.9664(9) A, space group I4/m. The symmetry of hollandite compounds depends on the ratio of the average ionic radius of the octahedral cations to that of the tunnel cations. Structures in which this ratio is >0.48 distort, reducing the tunnel volume, and thereby lowering the symmetry from tetragonal to monoclinic. The position occupied by a tunnel cation is determined primarily by the cation size. Relatively small cations, such as Ba2+ in priderite and Pb2+ in hollandite, displace from the special position, 2(a), to more stable sites that are at the sum of the ionic radii from the nearest O atoms. This study also indicates that the reduced form of Mn in hollandite and cryptomelane is Mn3+; the bond lengths suggest that the Mn3+ ion is more easily accommodated in the structures than the larger Mn2+.-J.E.C.
The redox chemistry of soil Mn is important in Mn uptake by plants, the movement of trace elements absorbed on or occluded in Mn-oxides, and the etiology of some soil-borne plant fungal diseases. The objectives of this study were to develop calibration curves for determining Mn oxidation states in moist soil samples using micro-x-ray absorption near-edge structure spectroscopy and to test the method on selected soils. Oxidation-state standards were prepared by mixing dry powders and a synthetic Na-birnessite, to obtain various Mn{sup 2+} mole fractions f(Mn{sup 2+}). Corundum (α-AlâOâ) was used as a diluent to prepare mixtures containing 50, 1000, and 100000 mg Mn/kg. Quantitative analysis of Mn oxidation state is possible using either the energy of the pre-edge peak at 6540 eV or a ratio based on the intensity of the Mn{sup 2+} white line peak at 6552.6 eV divided by the intensity of the Mn{sup 2+} white line peak at 6560.9 eV. The white line intensity ratio is more sensitive, with an estimated lower detection limit of 20 mg Mn/kg using a 300 by 300 μm spot, and predicts f(Mn{sup 2+}) with an accuracy of {+-}0.1 mole fraction (95% confidence interval) through most of its range. The f(Mn{sup 2+}) for four air-dried Indiana surface soils ranged from 0.26 to 0.44 {+-}0.1. Saturation and reduction for 5 d resulted in complete reduction of Mn in the soil matrix. 39 refs., 9 figs., 1 tab.
A B S T R A C T : A synthetic phyllomanganate saturated with a series of primary alkylammonium cations has been examined using XRD, chemical analysis and X-ray photoelectron spectroscopy. A linear relationship exists between the basal spacing of the saturated alkylammonium-manganate and the hydrocarbon chain length in the interlayer, and from the gradient it is concluded that the alkyl chains are perpendicular to the manganate sheet. This orientation is a function of both the charge density and the presence of a layer of water molecules immediately adjacent to the manganate basal surfaces. Evacuation results in the loss of this interlayer water and the structure of the organo-manganate is considerably disrupted. The extent to which the interlayer arrangement can be reinstated by rehydration is dependent on the chain length of the saturating organo-cation. For cations of chain length > C6 the C contents suggest that cation in excess of the exchange capacity is present in the interlayer, but the absence of any compensating anion and the release of amine on evacuation suggests that the excess C arises from the presence of free amine.
Electron probe analyses on 30 areas of lithiophorite, (Al,Li)MnO2(OH)2, from five Australian localities indicate wide variations in its content of Ni, Co, Cu and Zn. The amount of these elements varies inversely with the Al content, although there is a marked change at Al2O3 approx 18%, suggesting two varieties with different concentrations of transition elements. The variation in Al and transition elements is explicable if lithiophorite is considered as an irregular mixed-layer-lattice intergrowth of pure lithiophorite with members of the recently recognized asbolan-type minerals (M.A. 82M/0648). -R.A.H.
Microprobe analyses of 35 specimens of todorokite (checked by XRD, TEM and IR techniques) from various localities lead to the conclusions: 1) Ca is not essential and is absent from some terrestrial todorokites, being replaced by Ba, 2) Co can occur in the todorokite structure, 3) the concentration of Cu and Ni in todorokite appears to be strongly influenced by the mode of occurrence, these elements being low to absent in terrestrial todorokite.-R.A.H.
A manganese pan near Birness contains grains of an optically uniaxial negative mineral near (Na 0·7 Ca 0·3 )Mn 7 O 14· 2·8H 2 O, giving an X-ray powder pattern similar to that of synthetic materials described as ‘manganous manganite’ and δ-MnO 2 . Material giving a similar pattern has been described from a natural occurrence in Canada, but no mineral name was assigned; the name birnessite is now proposed. The mineral is probably formed by air-oxidation of manganous oxides under alkaline conditions.
The effect of pH and metal ion concentration on the adsorption of Cu, Co, Cd, Mn, Ni and Zn onto manganese oxides was investigated. The oxides used in the experiments were deposited around individual sand grains in water treatment filter beds in NE Scotland and show reproducible adsorption profiles regardless of location or age. The oxides remained amorphous throughout the four-year study period, and show an inferred pHZPC of 1.5. Metal adsorption increases towards more alkaline pH. The adsorption series Co > Cu > Cd > Zn > Mn > Ni is shown at pH 3 and Cu > Co > Cd > Mn > Zn > Ni at pH 6. Changing the concentration of the metal ions in solution leads to an increase in the mass of metal adsorbed, though the relationship is not linear as the proportion of metal taken up falls as concentration rises. Adsorption from an artificial seawater solution shows a significant reduction in the amount of metal taken up in all cases except Cu which shows an adsorption profile comparable with that in deionized water. The linear Freundlich isotherm accurately and reproducibly models the adsorption profile of all metals at each pH and concentration examined. The data do not, however, replicate the enrichment sequence observed in manganese nodules. The study demonstrates that for the enrichments observed in manganese nodules to be attained, the active oxide surface must be replenished by regular precipitation of fresh oxide material to enable continued adsorption to take place.
Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. These processes are discussed.
Terrestrial manganese deposits formed by hydrothermal, sedimentary and supergene processes. Ancient analogues of modern oceanic hydrothermal deposits formed in spreading centre and subduction-related settings and those deposited from terrestrial hot springs are discussed. Sedimentary Mn oxide deposits formed in shallow water at the margins of stratified oceans above the redoxcline during sea-level changes. Mn carbonate deposits probably formed by diagenesis through Mn oxyhydroxide reduction coupled with organic matter oxidation. Climatic variation, and basin water stratification, responsible for Mn concentration, were manifestations of atmospheric CO2 content prompted by tectonism. Supergene manganese enrichment in continental weathering profiles was mainly dictated by climate, topography and drainage systems.
The mineralogical composition of the surface soil horizon (0-15 cm) of Wahiawa soil (Tropeptic Eutrustox) was investigated by X-ray diffraction (XRD), high gradient magnetic separation (HGMS), transmission electron microscopy (TEM), and infrared methods. The concentration of lithiophorite decreased with particle size and none was present in the clay fraction as indicated by XRD. Lithiophorite was further concentrated from the crushed sand-sized fraction by HGMS. Hexagonal, electron-dense, often twinned lithiophorite particles were identified by electron diffraction. Differential infrared (DIR) spectra obtained by dissolving Mn oxides in acidified hydroxylamine hydrochloride (HAHC) indicated lithiophorite as the HAHC-soluble Mn-phase. Lithiophorite compositiion, as revealed by chemical analysis of the HAHC extracts, consisted of appreciable amounts of Mn, Al, Zn, Co and Mg, and less than stoichiometric amounts of Li. Sodium hydroxide treatment apparently altered the lithiophorite, as revealed by the DIR spectrum of the hydroxylamine-soluble fraction of the NaOH-treated sample compared with the untreated sample. The high crystallinity of the lithiophorite was suggested by its resistance to chemical dissolution and narrow X-ray diffraction lines. No evidence for the presence of todorokite or birnessite was found, contrary to earlier reports. Examination of sand-sized nodules by scanning electron microscopy indicated large (2-5 �m) platy lithiophorite crystals at the surface of these nodules. Electron microprobe analysis of these platy particles indicated iron enrichment near the surface. The freshly fractured nodule surface revealed numerous unaltered platy crystals of lithiophorite filling the veins of the nodule.
The mineralogical and chemical compositions of 28 manganese nodules from Australian soils were studied. Specific manganese minerals were identified in 26 of these after extraction and concentration from the associated soil minerals; 10 were lithiophorite Li2A18 (Mn2+, Co, Ni)2, Mn4+10O35.14H2O; 10 were birnessite, (Ca, Mg, Na2, K2)x Mn4+Mn2+(O, OH)2; 3 were hollandite, Ba(Mn4+, Fe3+)8O16; 1 was todorokite (Mn2+, Mg, Ca)Mn4+6O13.3-4H2O; 1 was pyrolusite MnO2; 1 contained both lithiophorite and hollandite. With the possible exception of pyrolusite, all samples were found to contain varying amounts of Ni, Co, Mg, Ba, Al, K, Na, Fe, and Ca. Although there was overlap in the chemistry of the birnessite and lithiophorite groups, the mean concentrations of aluminium, iron, and lithium were lower and the mean concentration of calcium and magnesium higher in the former group. Pure manganese oxides and hydroxides appear to be quite rare as secondary soil minerals. Lithiophorite occurred mainly in neutral to acid subsurface soils, whereas birnessite, although found in both acid and alkaline soils, was more common in alkaline surface horizons. The average crystallite size of the manganese mineral aggregates was quite small, being of the order of 0.02 µm for birnessites and 0.1 µm for the lithiophorites.
The distribution of ammonium citrate-leachable lead, zinc and cadmium among size fractions in stream sediments is strongly influenced by the presence of hydrous Mn-Fe oxides in the form of coatings on sediment grains. Distribution curves showing leachable metals as a function of particle size are given for eight samples from streams in New York State. These show certain features in common; in particular two concentrations of metals, one in the finest fractions, and a second peak in the coarse sand and gravel fraction. The latter can be explained as a result of the increasing prevalence and thickness of oxide coatings with increasing particle size, with the oxides serving as collectors for the heavy metals. The distribution of Zn and Cd in most of the samples closely parallels that of Mn; the distribution of Pb is less regular and appears to be related to Fe in some samples and Mn in others. The concentration of metals in the coarse fractions due to oxide coatings, combined with the common occurrence of oxide deposition in streams of glaciated regions, raises the possibility of using coarse materials for geochemical surveys and environmental heavy-metal studies.
Sequential digestions of Fe-Mn oxide coated boulders collected upstream and downstream from the Magruder mine, Lincoln Co., Georgia, indicate probable partitioning relationships for Zn, Cu, Pb, Co, and Ni with respect to Mn and Fe. Initial digestion with 0.1M hydroxylamine hydrochloride (Hxl) in 0.01M HNO3 selectively dissolyes Mn oxides, whereas subsequent digestion with 1:4 HCl dissolves remaining Fe oxides.The results indicate that partitioning is not constant, but varies systematically with respect to the location of metal-rich waters derived from sulfide mineralization. Upstream from the mineralized zone Zn and Ni are distinctly partitioned to the Fe oxide component and Co and Cu are partitioned to the Mn oxide component. Immediately downstream from the mineralized zone, Mn oxides become relatively more enriched in Zn, whereas Fe oxides are relatively more enriched in Cu, Co, and Ni. Analytical precision for Pb is poor, but available data suggests it is more closely associated with Fe oxides.For routine geochemical surveys utilizing coated surfaces, a one-step digestion method is probably adequate. Parameters useful for detecting sulfide mineralization are metal concentrations normalized to surface area or various ratios (e.g. Zn/(Mn + Fe), Cu/Mn, Pb/Fe). Ratios can be obtained much faster, and at lower analytical costs than conventional analysis of stream sediment.
The mineralogy of 45 managanese nodules from a range of marine environments is described. 10 Å manganite is shown to be the principal mineralogical phase in 9 nodules from shallow-water, continental-margin environments, whereas δ MnO2 is the principal mineralogical phase in 35 nodules from the Carlsberg Ridge, Indian Ocean. The phase relationships appear to be controlled by the redox characteristics of the sedimentary environment rather than the kinetics of nucleation or mineralogical ageing phenomena. The present data give no evidence to support the influence of submarine volcanism on nodule mineralogy.
The Pinal creek drainage basin in Arizona is a good example of the principal non-coal source of mining-related acid drainage in the U.S.A., namely copper mining. Infiltration of drainage waters from mining and ore refining has created an acid groundwater plume that has reacted with calcite during passage through the alluvium, thereby becoming less acid. Where O2 is present and the water is partially neutralized, iron oxides have precipitated and, farther downstream where the pH of the stream water is near neutral, high-Mn crusts have developed.
Depth profiles of the naturally-occurring radionuclides 238U, 234U, 226Ra, 228Ra and 228Th were obtained in two diverse anoxic marine environments; the permanently anoxic Framvaren Fjord in southern Norway and the intermittently anoxic Saanich Inlet in British Columbia. Concentrations of total H2S were over three orders of magnitude greater in the anoxic bottom waters of Framvaren Fjord compared to those in Saanich Inlet.In Framvaren Fjord, the O2/H2S interface was located at 17 m. While dissolved 238U behaved conservatively throughout the oxic and anoxic water columns, concentrations based on the 238U/salinity ratio in oxic oceanic waters were almost 30% lower. Dissolved 226Ra displayed a sharp maximum just below the O2/H2S interface, coinciding with dissolved Mn (II) and Fe (II) maxima in this zone. It is suggested that reductive dissolution of Fe-Mn oxyhydroxides remobilizes 226Ra in this region.In Saanich Inlet, the O2/H2S interface was located at 175 m. Dissolved 238U displayed a strongly nonconservative distribution. The depth profiles of dissolved 226Ra and 228Th correlated well with the distribution of dissolved Mn (II) in the suboxic waters above the O2/H2S interface, suggesting that reduction of particulate Mn regulates the behavior of 226Ra and 228Th in this region.Removal residence times for dissolved 228Th in the surface oxic waters of both systems are longer than those generally reported for particle-reactive radionuclides in coastal marine environments. In the anoxic waters of Framvaren Fjord and Saanich Inlet, however, the dissolved 228Th removal residence times are quite similar to values reported for dissolved 210Pb in the anoxic waters of the Cariaco Trench and the Orca Basin. This implies that the geochemistries of Th and Pb may be similar in anoxic marine waters.
The mineralogy and genesis of the tetravalent manganese oxides present in the Groote Eylandt ore are discussed on the basis of recent mineralogical concepts. Their mechanisms of formation on Groote Eylandt are described in terms of primary sedimentation (formation of vernadite, romanechite, pyrolusite, todorokite); diagenesis (formation of pyrolusite); supergene processes (formation of cryptomelane and lithiophorite) and pedogenic processes (formation of chalcophanite and birnessite). These geochemical processes have resulted in the formation of deposits of metallurgical ore of a cryptomelane-pyrolusite mineralogy and a battery-active ore of vernadite-todorokite-pyrolusite mineralogy.
Iron content of the manganese sesquioxides as an indication of the temperature of formation of the ores in various localities.
Temperatures of formation, Postmasburg Field and Kalahari Field, lateral zoning. Manganese ores in both fields were precipitated
by solutions which moved from west to east. The main mineralization episode dates from the Proterozoic Era.--Modified journal
abstract.
High concentrations of palladium and platinum (average 75 ppm and 4 ppm, respectively) are associated with copper ores at the New Rambler mine. The ore deposit is of hydrothermal origin and occurs in metagabbroic rocks at the intersection of a mylonite zone, several closely spaced faults, and a major shear zone. Three principal mineral assemblages have been defined in the hypogene ore paragenesis: (1) an early assemblage consisting mainly of pyrite, with magnetite, pyrrhotite, pentlandite, and chalcopyrite as accessories; (2) and (3) copper-rich assemblages representing the main stage of ore deposition and consisting principally of chalcopyrite + pyrrhotite but differing in accessory platinoid and base metal minerals. Thermochemical data on mineral compatibilities suggest deposition of asesmblage 1 at temperatures in the vicinity of 335°C or somewhat higher and the principal mineralization with deposition of copper- and platinoid-rich assemblages at temperatures somewhat below 335°C. Ten platinum and palladium minerals are recognized in the ore. Eight of these minerals are bismutho-tellurides or tellurides. Pt and Pd apparently occur in the ore principally as their own minerals. A comparative study of the distribution and geochemical behavior of the precious metals Pt, Pd, Rh, Au, and Ag in the weathered portions of the deposit has shown that Pt and Rh are substantially enriched in the strongly oxidized ore horizons, possibly due to supergene processes. Pd and Ag have been extensively mobilized from the upper levels during weathering. Ag has undergone dramatic enrichment in the supergene sulfide zone, but Pd apparently has been removed from the system.